The new safety interlock device is for use in appliances such as household clothes washing machines and dryers for maintaining the access door locked at any time that a motor driven component such as the spin dry tub of a washing machine is being driven or is coasting to a stop. As is known, spinning for centrifugal drying is conducted at high speed and provides a chance for personal injury if it is accessible while still rotating.
A variety of systems are illustrated in the prior art for preventing opening of an access door while a component of an appliance such as a washing machine is in motion. One popular scheme is to use a mechanical latch which holds the door in closed position while at the same time actuating a switch that partially enables the motor circuit. A solenoid operator and latching mechanism is also provided for maintaining the cover latch locked until the solenoid is energized concurrently with de-energization of the motor in which case the latch becomes unblocked and can be released to open the door. An example of this basic approach is shown in U.S. Pat. No. 2,738,072.
The latter patent also shows another approach which is to use a bimetal element to effect latching and unlatching of an appliance cover or lid. The bimetal actuates a latch lever into selective engagement and disengagement with a hook latch element on the door. The bimetal element is adjacent a resistance heater element which is energized when the motor is energized and causes the bimetal element to effect latching of the cover. A separate switch is placed in a series circuit with the motor and this switch is closed when the door is closed. The bimetal heater is de-energized when the motor is de-energized by a timer switch which controls the drying cycle or by other means. When the bimetal has cooled sufficiently over an interval following termination of motor current, the bimetal is effective to unlatch the latch element and permit opening of the door. While the door is open, the switch is open so the motor is always prohibited from operating at this time.
Other examples of electromechanical or solenoid operated interlock mechanisms are illustrated in U.S. Pat. Nos. 2,618,282; 2,896,641 and 2,936,892. The solenoid operated cover lock devices shown in the prior art employ a large number of fixed and movable parts and are therefore costly and complex. Generally, they are not unitary devices which can be mounted easily and in a single operation during assembly of the appliance. The prior interlock mechanisms usually require mounting a switch in one location, a solenoid operator in another, a latch in another and then assembling linkages and springs to complete the mechanism. As is well known to those involved in manufacture of appliances, the cost of manufacturing and installing the multiple element interlock mechanisms has been unduly high. Moreover, their complexity increases the statistical probability of failure during the life of the appliance.